1. Field of the Invention
The present invention relates to a turbine plant compressor disc provided with a centripetal accelerator for the induction of turbine cooling air from the compressor.
2. Summary of the Prior Art
In engines cooled through the inside of the high pressure compressor rotor, the cooling air intended for the turbine discs and blades is generally taken from the flow path of the compressor through holes drilled in the rings of the compressor drum, and then directed towards the turbine through the inside of the drum.
These drilled holes suffer from the drawback of introducing bending stresses which limit the maximum radius of the ring which is acceptable. Such an arrangement is shown in French Patent No. 1 248 916. Bores are made in the rings of the drum between two discs, and air guide means in the form of a quadrant having a central rib is screwed or rivetted under the rings. This makes it necessary to drill, in addition to the holes for taking the cooling air, holes for the screws or rivets which further increase the bending stresses suffered by the drum, making more critical the employment of hammer fastening blades on the stages of the rotor.
Furthermore, the substantial mass of such fastenings would lead to excessive centrifugal stresses on the rim of a two-part compressor disc and would tend to move the two halves of the disc apart. The possibility of siting the ring as high as possible permits an effective bracing of the discs which opposes the separation of the disc-halves.
To avoid these drawbacks, European Patent No. 0 049 655 proposes a gas turbine cooling arrangement in which the turbine cooling air is taken in the plane of the disc carrying the compressor blades through bores situated in the platforms of the hammer fastening blades themselves.
The reduction of bending stresses resulting therefrom makes it possible to raise the drum fastenings on the disc to a radial level close to the rim. This arrangement is particularly advantageous to discs made up of two halves welded at the rim and permits the use of hammer-root blades which are often heavier but less expensive than the standard blades with pins. However, it has been observed that the presence of fins on the inside of each disc-half introduces asymmetrical centrifugal stresses which, in turn, bring about deformations of the disc-halves and may in the end cause a rupture of the disc in the region of the rim welding.
French Patent No. 2 552 164 proposes a solution to this problem by the use of a centripetal accelerator which has several sectors mounted in a removable manner in the space provided between the two halves of the compressor disc, each sector being made up of two half-shells having on their inner face ribs in the form of centripetal vanes by means of which the half-shells are assembled.
Using vanes which are not integral with the faces of the disc makes it possible to obtain smooth inner faces of the disc-halves. As a result, the two faces are substantially symmetrical and the centrifugal stresses are balanced.
However, it is a drawback of this arrangement that it does not permit supply of air through the rim of the disc from the space situated under the blade platforms, as the sectors of the accelerator extend inside the disc right out to the rim, which makes it necessary to take air in the central plane of the disc. Taking air in this way is not satisfactory as secondary stray flows cause pressure disturbance, and it is therefore preferable to take air downstream of the blades.
It is an object of the present invention to simplify the above described arrangements without exhibiting their drawbacks and to permit the taking of air downstream of the blades.
A further object of the invention is to provide a compressor disc with a centripetal accelerator in a form sufficiently simple to permit its easy construction in composite materials in order to achieve a reduction of mass overall.